1. Field of the Invention
The present invention relates to inset-molding. More specifically, the present invention relates to a semiconductor chip molding apparatus and to a method of detecting whether a lead frame is positioned properly in the same.
2. Description of Related Art
The manufacturing of semiconductor devices, known as chip packages, includes an assembly method in which chips are packaged once they have undergone an electrical die sorting (EDS) process in which individual chips having certain electrical and physical characteristics are sorted. Hence, only non-defective chips are packaged.
The assembly method includes a die bonding process of attaching the non-defective chip on a pad of a lead frame, a wire bonding process of electrically connecting bonding pads of the chip to inner lead tip of the lead frame via connector wires, a molding process of encapsulating the chip using an epoxy molding compound so as to protect the chip, the connector wires, the inner leads, and so on, and a forming process of finalizing the form of the chip package so that the chip package may be mounted on a printed circuit board (PCB).
The molding process is performed by a semiconductor molding apparatus. In this apparatus, an epoxy molding compound is heated and pressurized to assume a molten state. The molten compound is then injected into molding cavities to encapsulate semiconductor chips on lead frames set in position in the cavities.
The conventional semiconductor chip molding apparatus also has a sensing unit that determines whether the lead frames are properly positioned in the apparatus before the semiconductor chips are encapsulated with the epoxy molding compound. Thus, the sensing unit attempts to ensure that the molding process is performed properly.
FIG. 1 is a cross-sectional view of the conventional semiconductor chip molding apparatus.
Referring to FIG. 1, the conventional semiconductor chip molding apparatus 90 includes a lower platen 70, and an upper platen 80 opposed to the lower platen 70. A lower mold 50 is integrated with the lower platen 70, and an upper mold 60 is integrated with the upper platen 80.
The lower mold 50 includes a plurality of locater pins 53 at the periphery thereof. The locater pins 53 guide a lead frame 20 into position on the lower mold 50. A port block 55 is disposed at a central portion of the lower mold 50. The molding resin, such as an epoxy molding compound, is supplied through the port block 55 after the lead frame 20 has been set on the lower mold 50.
As mentioned above, the conventional semiconductor chip molding apparatus 90 further includes a sensing unit to determine whether the lead frame has been properly set on the lower mold 50. The sensing unit includes a sensing plate 57 and an approaching sensor 65. The sensing plate 57 and the approaching sensor 65 are disposed on corresponding portions of the lower platen 70 and the upper platen 80, respectively.
After the lead frame 20 is set on the lower mold 50, the upper platen 80 moves down until it contacts the port block 55 on the lower platen 70. During this time, the approaching sensor 65 senses the sensing plate 57 and calculates the distance C between the approaching sensor 65 and the sensing plate 57 to determine whether the lead frame 20 is properly set on the lower mold 50. When the calculated distance C between the lower mold 50 and the upper mold 70 is equal to the thickness d of the port block 55, the lead frame 20 is regarded as being properly set on the lower mold 50. On the other hand, when the distance C between the lower mold 50 and the upper mold 70 is greater than the thickness d of the port block 55, the lead frame 20 is regarded as being improperly set on the lower mold 50.
However, the conventional semiconductor chip molding apparatus has the following disadvantages.
First, the lead frame 20 can be detected as being improperly set on the lower mold 50 only when the lead frame 20 is disposed on the port block 55 as shown in portion B of FIG. 1. In other words, it is impossible to determine when the lead frame 20 has been set on the locater pins 53 as shown in portion A of FIG. 1. This is because the locater pins 53 penetrate the lead frame 20 under the pressure of the upper mold 60. As a result, the locater pins 53 seem as though they are properly inserted into side rail holes (850 in FIG. 3) of the lead frame 20. Therefore, even though the lead frame 20 is improperly set on the lower mold 50, the lead frame 20 is regarded by the sensing unit as being properly set on the lower mold 50.
In addition, even when the lead frame 20 has been placed over the port block 55 as shown in portion B of FIG. 1, the sensing unit can hardly detect the improper positioning of the lead frame 20 because the lead frame 20 is very thin, e.g., is only 5 mil to 10 mil thick.
Moreover, epoxy molding compound scrap, produced in the previous molding process, remains on the lower mold 50. The epoxy molding compound scrap affects the ability of the sensing unit to detect whether the lead frame 20 is properly set on the lower mold 20.
In the conventional semiconductor chip molding apparatus, the lead frame 20 is regarded as being improperly set on the lower mold 50 when the epoxy molding compound scrap has a thickness of more than 0.3 mm. However, the conventional semiconductor chip molding apparatus is calibrated to detect epoxy molding compound scrap having a thickness of more than 0.5 mm for the purpose of preventing the epoxy molding compound scrap from producing an abnormal operation. Thus, the ability of the apparatus to determine whether the lead frame is properly set on the lower mold is nominal. Consequently, the manufacturing yield is poor.
An object of the present invention is to overcome the above described problems and limitations of the prior art. More specifically, it is one object of the present invention to provide a semiconductor chip molding apparatus that can accurately and surely detect whether a lead frame is properly set in position. It is another object of the present invention to provide an inset-molding apparatus having an improved manufacturing yield.
In order to achieve the above object, the molding apparatus comprises an upper platen including an upper mold, a lower platen including a lower mold having a molding block defining at least one mold cavity; a controller that controls an operation of the semiconductor chip molding apparatus; and an electrical detector for forming an electrical circuit between the controller and the lead frame or other metal part to be inset-molded when the lead frame or metal part is oriented a certain way, i.e., improperly, on the lower mold.
The detector includes at least one detecting block positioned adjacent the molding block so as to contact the lead frame when the lead frame is improperly set on the molding block. The detecting block is electrically insulated from components of the molding apparatus, including the lower mold. A detecting wire connects the detecting block to the controller and transfers the electrical signal to the controller.
The detector further includes a connecting block connected to the detecting block. The connecting block includes a conductive spring or a screw disposed in contact the detecting block so as to transfer an electrical signal from the detecting block to the controller.
Another object of the present invention is to provide a method for use in operating an inset-molding apparatus, in particular, a method of operating a semiconductor chip molding apparatus, which accurately detects when a metal part such as a lead frame to be inset-molded is improperly positioned over the mold cavity.
The method comprises: setting the lead frame or other metal part to be inset-molded on a conductive lower mold of the molding apparatus; providing at least one electrically conductive detecting block adjacent the lower mold, and electrically insulating the at least one electrically conductive block from at least the lower mold; and subsequently imparting a voltage to at least the lower mold.
As a result, an electrical signal will flow from the detecting block when the lead frame or other metal part to be insert-molded rests on the detecting block. When such a signal is detected, therefore, the lead frame or other metal part is determined as having, for example, been improperly set on the molding block. The signal generated is detected by a controller and thereby used to control the further operation of the apparatus. In particular, the controller interrupts the operation of the molding apparatus when the monitoring of the detecting block for an electrical signal indicates that the part to be inset-molded is mis-positioned on the molding block relative to the mold cavity.